name: code-quality-principles description: iinkTS code quality checklist — centralization, DRY, short functions, mandatory tests. Invoke before commit, during refactor, code review, or when creating a new file. metadata: version: "1.0.0"

Code Quality Principles

Centralization

One source of truth per concept. src/utils/ for cross-cutting utilities, Abstract*/Base* classes for shared behavior. Before writing a utility function → grep src/utils/ first.

DRY

• 2 occurrences of the same logic → extract a function
• 3 occurrences of the same pattern → extract an abstraction
• Magic constant → extract (const NORMALIZATION_FACTOR = 1000)

Short functions

• Max 20 lines (ideal 10)
• One abstraction level per function
• Early return for failure cases
• Naming: is*/has*/can* (boolean), get*/find* (value), set*/update* (mutation)

// bad: mixes validation + normalization + transformation + rendering + side-effect
function processAndRenderStroke(stroke, canvas, options) { /* 30+ lines, 4 levels */ }
// good: each function one level
function isValidStroke(stroke) { return !!stroke?.pointerType && stroke.x.length > 0 }
function normalizeStroke(stroke) { return { ...stroke, x: normalizeArray(stroke.x) } }
function processStroke(stroke) { return isValidStroke(stroke) ? normalizeStroke(stroke) : null }

Unit tests (mandatory)

• Mirror architecture: test/unit/ mirrors src/
• Coverage ≥75% (branches/functions/lines/statements)
• Naming {ClassName}.test.ts
• Minimum per function: nominal case, error case, edge case (null/undefined/empty/zero)

Refactoring patterns

• Extract function: repeated condition → named function (isValidData)
• Extract constant: magic number → named const
• Replace conditional with polymorphism: if/else if on a type → interface + implementations

Checklist before commit

• [ ] No duplication
• [ ] Functions ≤20 lines, one abstraction level
• [ ] Explicit names (no comment needed)
• [ ] Early returns for failure cases
• [ ] Unit tests present, yarn test:unit --coverage ≥75%
• [ ] yarn typecheck clean